1. Field of the Invention
The present invention relates to a method and system for conditioning of intake air and/or exhaust gases for an internal combustion engine.
2. Description of Related Art
For many combustion engines, including various gasoline and diesel designs, it is beneficial to supply sufficient air to the combustion chamber for combusting all of the fuel in the combustion chamber. Complete combustion decreases fuel consumption, and reduces emissions such as hydrocarbons and carbon monoxide. Achieving complete combustion, however, requires operating the engine at a leaner air/fuel ratio than will provide the maximum power output. For example, for most gasoline engines, an air/fuel ratio of 15:1 to 16:1 yields optimal fuel efficiency, while the stoichiometric ratio is about 14.7:1, and maximum power is realized between about 12.5:1 and 13.5:1. Many modern engines control the air/fuel ratio depending on the engine operating conditions, operating more leanly at low power than at high.
Because combustion engines are limited to a fairly narrow range of optimal air/fuel ratios, an engine of a given size is limited by its design to a certain maximum power output. An engine's power is limited by the amount of fuel it can combust, which is, in turn, limited by the amount of air it takes in (airflow). The airflow of an engine depends on its displacement, engine speed (e.g., rpm), and volumetric efficiency. Displacement is generally fixed based on the engine design. Volumetric efficiency is defined as the amount of air taken in by an engine, divided by the theoretical maximum amount of air that can be taken in under the same conditions. It is seldom greater than about 80-85% for a naturally aspirated gasoline engine, and typically diminishes greatly at high engine speeds. For example, at 1000 rpm, an engine's volumetric efficiency may be 75%, at 2000 rpm 85%, and at 3000 rpm 60%.
It is theoretically desirable to have volumetric efficiency as high as 100%, or even greater, at all engine speeds. Generally, a well-designed engine with a high volumetric efficiently can be made lighter than an engine of comparable power having a lower volumetric efficiency. Volumetric efficiency is often raised using a turbocharger or supercharger to compress the engine's intake air. Volumetric efficiency can be increased to greater than 100% using such devices.
However, turbochargers and superchargers have their own disadvantages. For one thing, such devices are relatively expensive. More fundamentally, using compressed intake air inevitably results in a higher engine compression ratio than using natural aspiration in the same engine. This, in turn, causes higher engine stress that may shorten engine life, and/or may require increasing the mass of engine components or making other modifications to handle the higher stresses. In gasoline engines, higher compression ratios often necessitate the use of higher-octane (premium) gasoline, which is more expensive than regular gasoline. Another disadvantage is higher combustion temperatures, because the air/fuel mixture experiences increased compression heating prior to ignition. In turn, higher combustion temperatures may increase generation of undesired emissions, and in particular, nitrous oxides (NOx). Higher combustion temperatures may also increase engine temperature, shortening the engine life and/or requiring increasing the capacity of the engine's cooling system or making other modifications to handle the higher temperatures.
Many of the benefits of increased volumetric efficiency, without the disadvantages associated with compressing intake air, may be realized by enriching intake air with oxygen. Simply put, using oxygen-enriched intake air can increase the amount of oxygen available for combustion, without requiring any compression of intake air. However, there is presently no effective solution for enriching intake air with oxygen, without drawing oxygen from a finite source such as a bottle. To avoid the limitations of bottled oxygen, it would be preferable to enrich intake air with oxygen in a continuous process, using only ambient air as a feedstock. But present methods of separating oxygen from air are too heavy, too bulky, and/or two expensive for practical application with most combustion engines. It is desirable, therefore, to provide an oxygen-enrichment system for a combustion engine that is sufficiently compact, lightweight and cost-effective for use in many common engine applications. It is further desirable to provide an internal combustion engine incorporating an oxygen-enrichment system for conditioning intake air, thereby attaining benefits similar to turbocharging or supercharging, without the disadvantages associated with an increased compression ratio.